1. Field of the Invention
This invention relates to the field of video recording and playback systems. Specifically, this invention relates to a method and apparatus for locating a commercial within a video data stream.
Television programs are commonly recorded through the use of a Video Cassette Recorder ("VCR"). Recordation allows a user to either view a program at a later time or to simultaneously watch a program and retain a copy of it to view at a later time. When a VCR is used to create a copy of the program to be viewed at a later time, many users are not interested in the content of commercials or promotions that are interposed within the television program. Such a user generally skips through these commercials manually.
2. Description of the Related Art
A device designed to perform skipping autonomically, such as U.S. Pat. No. 5,151,788 to Blum, cues the VCR to stop recording upon the occurrence of a "black frame". A black frame is usually found immediately before and after a commercial segment. Such a device also discerns a change in "activity" of the images that are displayed on the screen. An activity is the rate of change in the luminance level between two different sets of frames. Commercials are generally filled with "activity". When a low amount of activity is detected, the commercial is deemed to have ended. A resumption in recording follows.
Unfortunately, an "activity" is not well defined and, therefore, it is difficult to determine exactly when an activity begins or ends. Any black screen will stop the VCR from recording. As long as there is subsequent "activity", the device will assume the presence of a commercial. Consequently, a black screen followed by an action sequence in a program can be misjudged and skipped as a commercial. Alternatively, a slow-paced commercial might be misjudged and recorded as a program.
Another technique for identifying a black frame such as disclosed in U.S. Pat. No. 4,314,285 by Bonner et al., senses a drop in the voltage level of the input signal below a threshold. Yet another technique, such as disclosed in U.S. Pat. No. 5,333,091 by Iggulden et al., is to record the entire program including any commercials. A notation is made whenever a black frame is broadcast. After recordation, a processor determines whether the time period in between black frames was a commercial or a program. This is accomplished by a simple formula. If the time period is less than 5 minutes, it's deemed to be a commercial. During playback, the device fast-forwards the tape past the areas determined to be commercials. Since the device must remember when to start and stop playback, a special tape must be used or a standard tape must be altered thereby increasing the system cost. Furthermore, two black frames within five minutes of each other is not necessarily representative of a commercial as this could occur during a dimly lit or dark scene.
In still another technique, such as disclosed in U.S. Pat. No. 5,668,917 to Lewine, commercials are identified based on matching images. Sequential frames which match too closely, are assumed to represent a commercial. Scenes typically found in a talk show or a sit-com, where the actors do not often move, can be misjudged as a commercial and skipped under this technique.
All of the prior art devices are deficient in that their methods for discerning whether a signal is a commercial are often inaccurate. If there is a black frame in the middle of a movie, most of these devices will mistake it for a commercial. Therefore, there is a need for a commercial detection device which can find a commercial more reliably.